Quarterly Financial Data (Unaudited) - Schedule of Quarterly Financial Data (Detail) - USD ($) $ / shares in Units, $ in Millions	3 Months Ended								12 Months Ended
	Sep. 28, 2018	Jun. 29, 2018	Mar. 30, 2018	Dec. 29, 2017	Sep. 29, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 30, 2016	Sep. 28, 2018	Sep. 29, 2017	Sep. 30, 2016
Quarterly Financial Information Disclosure [Abstract]
Total revenues	$ 801.6	$ 709.1	$ 729.9	$ 678.5	$ 721.8	$ 632.8	$ 663.2	$ 601.5	$ 2,919.1	$ 2,619.3	$ 2,593.7
Gross margin	338.7	313.6	318.5	302.8	305.8	265.5	275.6	267.0	1,273.6	1,113.9	1,104.7
Net earnings from continuing operations	116.8	72.5	73.2	(112.2)	78.6	69.9	69.5	8.0	150.3	226.0	322.3
Net (loss) earnings from discontinued operations					0.0	0.0	(13.3)	6.5	0.0	(6.8)	77.4
Net (loss) earnings attributable to Varian	$ 116.4	$ 72.6	$ 73.2	$ (112.3)	$ 78.6	$ 69.7	$ 56.3	$ 13.9	$ 149.9	$ 218.5	$ 399.3
Net earnings (loss) per share from continuing operations - basic (in dollars per share)					$ 0.86	$ 0.76	$ 0.75	$ 0.08	$ 1.64	$ 2.44	$ 3.38
Net earnings (loss) per share from discontinued operations - basic (in dollars per share)					0.00	0.00	(0.15)	0.07	0.00	(0.08)	0.81
Net earnings per share - basic (in dollars per share)	$ 1.27	$ 0.79	$ 0.80	$ (1.22)	0.86	0.76	0.60	0.15	1.64	2.36	4.19
Net earnings (loss) per share from continuing operations - diluted (in dollars per share)					0.85	0.75	0.74	0.08	1.62	2.42	3.36
Net earnings (loss) per share from discontinued operations - diluted (in dollars per share)					0.00	0.00	(0.14)	0.07	0.00	(0.07)	0.80
Net earnings per share - diluted (in dollars per share)	$ 1.26	$ 0.79	$ 0.79	$ (1.22)	$ 0.85	$ 0.75	$ 0.60	$ 0.15	$ 1.62	$ 2.35	$ 4.16
Tax benefit related to change in law related to the Act	$ (7.1)			$ 207.1					$ 164.6
Loss on hedges related to acquisition-related activities		$ 13.3	$ 16.4
Impairment charges		11.0	$ 11.1		$ 13.1			$ 38.3	22.4	$ 51.4	$ 2.2
Acquisition costs		8.4							15.7
Breakup fee from Sirtex		$ 9.0
Tax benefit due to partial release of a valuation allowance	$ 8.0
Provision for doubtful accounts receivable								$ 37.8	$ 4.0	$ 43.7	$ 3.5